Photoinduced dynamics in an exchange-coupled trinuclear iron cluster

Abstract

We present a joint experimental and computational study of the trinuclear basic carboxylate iron complex FeIII2FeIIO(CH3CO2)6(H2O)3, which is a model system for understanding photoinduced ultrafast spin dynamics in magnetic iron-based transition metal oxides. We have carried out femtosecond optical transient absorption spectroscopy of molecules in solution at room-temperature exciting either at 400 or 520 nm and observed a long-lived excited-state absorption (ESA) signal from ca. 400–670 nm. The ESA signal is composed of several broad un-resolved bands at 405, 440 and 530 nm. The decay dynamics are complicated and three exponentials with corresponding decay time constants of τ1=360±30 fs, τ2=5.3±0.6 ps, τ3=65±5 ps and a constant offset (τ4>500 ps) were needed to fit the data over the full wavelength range. The data indicate that the lowest excited state is populated within the duration of the excitation pulse (<120 fs). Highly correlated coupled-cluster calculations can satisfactorily reproduce the experimental vibrational spectrum and highlight the role of the μ3-oxo bridge connecting the Fe ions to create a highly correlated ground-state and identify the excited state as having a mixture of both charge-transfer and ligand-field/d-orbital characters.